So I understand that the way we place seams in this tutorial is done to support the normal map bake. When it comes to unwrapping in general, we could get away with a lot less seams. There are an awful lot of separate, tiny uv islands in the final unwrap. This is necessary for the normal map bake, but isn't this going to cause a lot of noticeable seams in tiling textures or even when painting across different uv shells in something like Substance Painter? From what I understand you would want to place as few seams as possible (while minimizing distortion), and preferably only where it makes sense.
You're totally right - for objects without hard surface normal maps it's definitely best to use as few seams as possible. From what I've tried it's not usually worth it to make a separate unwrap for the other textures because #1 it increases the file size of the asset and #2 the second unwrap will still have a lot of seams since by nature the object is made up of a lot of sharp angles anyway, so it will only be marginally better.
You shouldn't notice the seams when painting across shells in Blender or Substance, but it will mess with tiled textures if you use UV projection instead of Triplaner projection.